Common names: EIA-449, RS-449, ISO 4902
Primary channel
 (at the DTE)
 (at the DTE)
 (at the DCE)
 (at the DCE)
CORRECT?
37 PIN D-SUB MALE at the DTE (Computer).
37 PIN D-SUB FEMALE at the DCE (Modem).
| Pin | Name | V.24 | Dir | Description | Type | 
|---|---|---|---|---|---|
| 1 | 101 |  | Shield | Ground | |
| 2 | SI | 112 |  | Signal Rate Indicator | Control | 
| 3 | n/a | n/a | unused | ||
| 4 | SD- | 103 |  | Send Data (A) | Data | 
| 5 | ST- | 114 |  | Send Timing (A) | Timing | 
| 6 | RD- | 104 |  | Receive Data (A) | Data | 
| 7 | RS- | 105 |  | Request To Send (A) | Control | 
| 8 | RT- | 115 |  | Receive Timing (A) | Timing | 
| 9 | CS- | 106 |  | Clear To Send (A) | Control | 
| 10 | LL | 141 |  | Local Loopback | Control | 
| 11 | DM- | 107 |  | Data Mode (A) | Control | 
| 12 | TR- | 108.2 |  | Terminal Ready (A) | Control | 
| 13 | RR- | 109 |  | Receiver Ready (A) | Control | 
| 14 | RL | 140 |  | Remote Loopback | Control | 
| 15 | IC | 125 |  | Incoming Call | Control | 
| 16 | SF/SR+ | 126 |  | Signal Freq./Sig. Rate Select. | Control | 
| 17 | TT- | 113 |  | Terminal Timing (A) | Timing | 
| 18 | TM- | 142 |  | Test Mode (A) | Control | 
| 19 | SG | 102 |  | Signal Ground | Ground | 
| 20 | RC | 102b |  | Receive Common | Ground | 
| 21 | n/a | n/a | unused | ||
| 22 | SD+ | 103 |  | Send Data (B) | Data | 
| 23 | ST+ | 114 |  | Send Timing (B) | Timing | 
| 24 | RD+ | 104 |  | Receive Data (B) | Data | 
| 25 | RS+ | 105 |  | Request To Send (B) | Control | 
| 26 | RT+ | 115 |  | Receive Timing (B) | Timing | 
| 27 | CS+ | 106 |  | Clear To Send (B) | Control | 
| 28 | IS | n/a |  | Terminal In Service | Control | 
| 29 | DM+ | 107 |  | Data Mode (B) | Control | 
| 30 | TR+ | 108.2 |  | Terminal Ready (B) | Control | 
| 31 | RR+ | 109 |  | Receiver Ready (B) | Control | 
| 32 | SS | 116 |  | Select Standby | Control | 
| 33 | SQ | 110 |  | Signal Quality | Control | 
| 34 | NS | n/a |  | New Signal | Control | 
| 35 | TT+ | 113 |  | Terminal Timing (B) | Timing | 
| 36 | SB | 117 |  | Standby Indicator | Control | 
| 37 | SC | 102a |  | Send Common | Ground | 
Note: Direction is DTE (Computer) relative DCE (Modem).
| Name | Description | Function | 
|---|---|---|
| AA | Shield Ground | Also known as protective ground. This is the chassis ground connection between DTE and DCE. | 
| AB | Signal Ground | The reference ground between a DTE and a DCE. Has the value 0 Vdc. | 
| BA | Transmitted Data | Data send by the DTE. | 
| BB | Received Data | Data received by the DTE. | 
| CA | Request To Send | Originated by the DTE to initiate transmission by the DCE. | 
| CB | Clear To Send | Send by the DCE as a reply on the RTS after a delay in ms, which gives the DCEs enough time to energize their circuits and synchronize on basic modulation patterns. | 
| CC | DCE Ready | Known as DSR. Originated by the DCE indicating that it is basically operating (power on, and in functional mode). | 
| CD | DTE Ready | Known as DTR. Originated by the DTE to instruct the DCE to setup a connection. Actually it means that the DTE is up and running and ready to communicate. | 
| CE | Ring Indicator | A signal from the DCE to the DTE that there is an incomming call (telephone is ringing). Only used on switched circuit connections. | 
| CF | Received Line Signal Detector | Known as DCD. A signal send from DCE to its DTE to indicate that it has received a basic carrier signal from a (remote) DCE. | 
| CH/CI | Data Signal Rate Select (DTE/DCE Source> | A control signal that can be used to change the transmission speed. | 
| DA | Transmit Signal Element Timing (DTE Source) | Timing signals used by the DTE for transmission, where the clock is originated by the DTE and the DCE is the slave. | 
| DB | Transmitter Signal Element Timing (DCE Source) | Timing signals used by the DTE for transmission. | 
| DD | Receiver Signal Element Timing (DCE Source) | Timing signals used by the DTE when receiving data. | 
| IS | terminal In Service | Signal that indicates that the DTE is available for operation | 
| NS | New Signal | A control signal from the DTE to the DCE. It instructs the DCE to rapidly get ready to receive a new analog signal. It helps master-station modems rapidly synchronize on a new modem at a tributary station in multipoint circuits | 
| RC | Receive Common | A signal return for receiver circuit reference | 
| LL | Local Loopback / Quality Detector | A control signal from the DTE to the DCE that causes the analog transmision output to be connected to the analog receiver input. | 
| RL | Remote Loopback | Signal from the DTE to the DCE. The local DCE then signals the remote DCE to loopback the analog signal and thus causing a line loopback. | 
| SB | Standby Indicator | Signal from the DCE to indicate if it is uses the normal communication or standby channel | 
| SC | Send Common | A return signal for transmitter circuit reference | 
| SF | Select Frequency | A signal from the DTE to tell the DCE which of the two analog carrier frequencies should be used. | 
| SS | Select Standby | A signal from DTE to DCE, to switch between normal communication or standby channel. | 
| TM | Test Mode | A signal from the DCE to the DTE that it is in test-mode and can't send any data. | 
| Reserved for Testing | 
| Contributor: | Joakim Ögren | 
| Source: | RS449 Page at Connectivity Knowledge Platform (Made IT) | 
  Copyright © The Hardware Book Team 1996-2004.
  May be copied and redistributed, partially or in whole, as appropriate.
  Document last modified: 2002-01-13